How to make a longer keypress result in a higher jump.

"I found just a few minutes to work on my 8-bit-style Phaser platformer since the weekend. Just about everyone in my family is sick in some way, including myself. So with my limited time I decided to fine-tune the jumps.

In my really basic code so far, a jump was accomplished by hitting space on the keyboard. If the frog was on the ground while space was pressed, the frog's y-velocity was set to a constant number. This worked fine, but it resulted in every jump being the same height. Tapping the spacebar for a millisecond caused the same jump as holding down the key for ten seconds. Well, actually holding down the key caused the frog to jump over and over and over again. I wanted to fix that too.

I was looking for a way to make a longer keypress result in more height, up to a limit. After reading a few ideas tossed out there by other people on the Internet, I decided on what to do."